The thermodynamic method used in nearly all air conditioners, refrigerators and heat pumps is the vapor compression cycle also called the refrigeration cycle. The basic cycle uses four primary components: a compressor, a condenser, an expansion device, and an evaporator. Some systems may use additional components such as a receiver, additional heat exchangers, two or more compressors, an accumulator, other specialized components, such as, but not limited to, a liquid vapor separator, a vortex separator, a surge tank, refrigerant reservoir, or vessel. The four primary components are piped in series to form a closed loop system that carries out the changes in temperature, pressure, and state of the working fluid, which may be refrigerant, which forms the basic vapor compression cycle. Furthermore, within air conditioners, refrigerators, and heat pumps, outside of the refrigeration cycle there are typically ancillary components that move the desired heat transfer medium, such as the blowing of air or of flowing of water that is to be cooled or heated. The heat transfer medium may be moved across the primary heat exchangers, which are the condenser coil and the evaporator coil. In addition, there is typically a control circuit that energizes and de-energizes the driven components, including the compressor, fan motors, pump motors, damper actuators, and valves. The driven components are energized or de-energized to meet a desired temperature, ventilation, humidity or other set point or operating parameters.
The efficiency of vapor compression cycles is numerically described by an energy efficiency ratio (EER) or a coefficient of performance (COP). The EER generally refers to the air conditioning, refrigerating, or heating system and is the ratio of the heat absorbed by the evaporator cooling coil over the input power to the equipment, or conversely for heat pumps, the rate of heat rejected by the condenser heating coil over the input power to the equipment. EER is defined as the ratio of cooling or heating provided to electric power consumed, in units of Btu per hour per watt. EER varies greatly with cooling load, refrigerant level, and airflow, among other factors. The COP generally refers to the thermodynamic cycle and is defined as the ratio of the heat absorption rate from the evaporator over the rate of input work provided to the cycle, or conversely, for heat pumps, the rate of heat rejection by the condenser over the rate of input work provided to the cycle. COP is a unit-less numerical ratio.
In addition, there is a standard weighted average of EER at four conditions known as the integrated energy efficiency ratio (IEER), which relates to an estimation of the energy efficiency over conditions experienced during a cooling season. Also, there is the seasonal energy efficiency ratio (SEER) that is used instead of the IEER for smaller air conditioning units. Either lowering capacity or increasing power manifest in reduced energy efficiency and a reduced EER, COP, IEER, or SEER. Increasing capacity without increasing power, or reducing power without decreasing capacity, or both increasing capacity and reducing power will manifest in an increased EER, COP, IEER, or SEER.
An energy management system for refrigeration systems is disclosed by Cantley (U.S. Pat. No. 4,325,223) and relies on inference of energy efficiency rather than a direct measurement. The inference is based on relative comparison of compressor power data and other system parameters stored in memory. The system of Cantley does not make control adjustments according to the system energy efficiency ratio, rather it controls evaporative cooling.
A system disclosed by Spethmann (U.S. Pat. No. 4,327,559) applies only to chilled water systems. The disclosure of Spethmann balances the trade-off between colder chilled water and faster fan airflow using ratio relays.
A method disclosed by Enstrom (U.S. Pat. No. 4,611,470) also applies only to chilled water systems. The method of Enstrom is for performance control of heat pumps and refrigeration equipment and depends on the chilled water temperature.
A system disclosed by Bahel, et al. (U.S. Pat. No. 5,623,834) is directed to diagnostics and fault correction. Only the fan speed and thermostatic expansion valve are controlled based on a relative comparison of two temperatures and the thermal load calculated via a thermostat.
Cho, et, al (U.S. Pat. No. 6,293,108) discloses methods for separating components of refrigerant mixtures to increase energy efficiency or capacity.
Chen, et al. (U.S. Pat. No. 7,000,413) discloses control of a refrigeration system to optimize coefficient of performance (COP), but there is no description of how the COP is determined. Chen discloses adjusting COP to achieve a reference COP stored in memory and does not optimize the COP. The primary application of Chen, et al. is transcritical systems using carbon dioxide refrigerant. Chen, et al. does not disclose an embodiment for measurement of the refrigerant flow rate. Chen, et al. discloses only adjusting the water flow rate and the expansion valve.
Automatic refrigerant charge adjustment methods are disclosed by Kang, et al. (U.S. Pat. No. 7,472,557), Murakami, et al. (U.S. Pat. No. 8,056,348), and McMasters, et al. (U.S. Pat. No. 8,272,227). These references disclose methods to adjust a charge to match published charging tables, reference temperatures, or pressure values.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.